1. Field of the Invention
This invention relates generally to devices for sampling flowing fluids and, more particularly, to such devices which operate within a closed loop system and which are capable of sampling easily compressible gases.
2. Prior Art
In industrial chemical plants, as well as other industrial process operations, it is often necessary to obtain samples of fluids flowing in pipelines or various other types of vessels. Often, such fluids are of a hazardous nature, requiring that exposure of personnel to the sample be minimized or eliminated. In most applications when a sample is taken from a line flowing under pressure, samples are taken in sample cylinders. Such cylinders are well-known in the art. A typical cylinder is usually provided with a valve on either end, allowing a sample to be encased therein.
Various methods have been attempted in the art to safely force the sample into the cylinder. One method is to simply connect one end of the cylinder to the line containing the fluid, open the valve at the connected end and bleed the other end of the cylinder using the opposite valve until the cylinder is full of sample and entrained gases are displaced. This method obviously has its limitations with hazardous materials, since the bleeding step offers the possibility of exposing sampling personnel to the sample (a clear violation of current federal regulations). Other methods create a vacuum in the cylinder; elaborate means such as mercury, glycol or water displacement are also used. All of the prior art methods are prone to failure as well as exposure of sampling personnel to the sample. Further, these methods do not always result in a truly representative sample being contained in the cylinder or the sample container.
Stringent environmental regulations have resulted from an increasing concern for the safety of sampling personnel as well as exposure or discharge of hazardous materials to the atmosphere. Regulatory and safety concerns have thus severely limited sampling, resulting in elaborate and expensive containment schemes. Nevertheless, monitoring of industrial processes must still take place. Highway tank trailers, railroad cars or marine transport tanks, such as tankers or barges carrying hazardous materials such as liquified petroleum gases, ammonia, ethylene oxide or other liquids or gasses under pressure are still sampled by an operator filling a sample cylinder by any one of several means known in the art, and previously mentioned in this application. These methods expose the operator to the fluid being sampled or require the taking of elaborate safety precautions and the wearing of bulky and often cumbersome safety equipment.
In some cases where the fluid which is to be sampled is an easily compressible gas (such as propylene or butadiene), the fluid is in liquid form when sampled. However, ambient heating of the sample cylinder will result in expansion of the sample, creating hazardous vapor pressures within the sample cylinder, possibly causing the cylinder to burst. In order to accommodate safe sample cylinder transportation, a desired amount of fluid from the cylinder is released, or bled, leaving room for safe expansion (commonly referred to as "cylinder outage") of the sample fluid remaining in the cylinder. This is usually accomplished using a dip tube, which attaches to either the inlet or the outlet of the cylinder and extends a desired distance into the cylinder. In the past, the person bleeding the sample simply oriented the dip tube upward and opened the valve on the dip tube end of the sample cylinder, bleeding the sample fluid until liquid was no longer visible, indicating that the liquid level in the cylinder was below the end of the dip tube. Prior to the existence of environmental control regulations, the bleeding procedure was often simply directed into the atmosphere. Now, the bleeding step must be accomplished by transporting the sample cylinder to and bleeding waste fluids into a disposal line, such as a flare line. The presence of gas or liquid in the discharge of the sample cylinder into the disposal line can be visually monitored by placing a sight glass in line between the sample cylinder outlet and the disposal line. A serious safety problem still exists with such a system in that the sample container must be disconnected while full of dangerously expansive fluid and transported to a discharge facility, endangering sampling personnel and the environment. Further, such a disposal procedure may introduce oxygen into the disposal line, creating a serious danger of explosion.
The prior art devices have not managed to economically provide the necessary safety while maintaining the integrity of the sample and clearly demonstrate the need for the present invention.